1. Field of the Invention
The present invention relates to servo positioning systems in which only sampled position data is available for feedback control.
2. Description of Prior Art
A typical positioning application to which the present invention can be applied is in connection with maintaining a magnetic head centered on information-bearing concentric tracks in a maqnetic disk file of the so-called "sector-servo" type. In such a file, servo position reference information is recorded in a plurality of spaced sectors interleaved between larger sectors on which the data is recorded. An advantage of such a system is that the servo information is contiguous with the recorded data so that the data tracks of interest can be followed with greater accuracy than with a separate dedicated servo surface and thus packed closer together. The servo sectors must be sampled at times defined by clock signals to enable a position error to be generated for track following purposes.
In some sector servo systems, the servo tracks in the sector portions are in the form of blocks of servo information, one set of blocks on one track being identified as block A signals and an adjacent track contains blocks identified as block B signals. The boundary between adjacent servo blocks is aligned with a data track center in the following data portion of the disk. Track following to maintain the head positioned over the data track center is accomplished by positioning the head near the desired location (by track accessing circuitry which does not form part of the present invention) and then reading and comparing the signals recorded in the servo blocks on adjacent servo tracks in the sector. When the head is located over the data track center, it will receive equal signals from block A signals and block B signals, and integration of the energy level of the signals and the comparison of these energy levels will result in a null condition, indicating that the head is located on the data track centerline. If the head is located off the data track centerline, the head will be located over more of one type of servo block than the other adjacent type so that the signals from the two types of blocks will not be equal, and energy integration and comparison of the two types of signals will result in the generation of a position error signal (PES) which can be used in the servo system to move the head toward the proper position over the data track centerline.
In sector servo systems, the servo information detected during reading of the servo information is stored and utilized during the interval that the head is over the subsequent data portion of the record to maintain the head over the data track centerline.